覆盖原来的List

//list截取功能

List<String> old_list= coll.distinct("_id", query);//MongoDB查询出一条list

List<String> new_list= new ArrayList<String>();
int i = 0;
System.out.println("我是未处理的list：" + old_list);
for (String list : old_list) {
if (null != list && "" != list) {
String str = list.substring(0, 5);
new_list.set(i, str);
}
i++;
}
System.out.println("我是处理过后的list" + new_list);